GST Calculator — intra- vs inter-state.

Add GST (exclusive mode): the amount you enter is the base value of the supply. GST is added on top.

GST = Base × (Rate / 100)
Total invoice = Base + GST

Reverse GST (inclusive mode): the amount you enter already includes GST. We back-calculate the base.

Base = Total × (100 / (100 + Rate))
GST = Total − Base

Intra-state supplies (supplier and place-of-supply in the same state): GST is split equally between Central GST (CGST) and State GST (SGST), each at half the headline rate.

Inter-state supplies (supplier and place-of-supply in different states): GST is collected as a single Integrated GST (IGST) at the full headline rate. The Centre subsequently apportions the state share to the destination state.

Place-of-supply rules under the IGST Act (Sections 10–14) determine intra- vs inter-state classification — not just the location of the parties. For services, the rules differ by category. When in doubt, talk to us.

Reverse charge (Section 9(3) / 9(4)): for specified categories of supply, the registered recipient discharges the GST liability instead of the supplier. Common triggers include goods-transport agency services, legal services from advocates, director sitting fees, and notified intra-state purchases from unregistered suppliers. The CGST/SGST or IGST split rule (intra- vs inter-state) is the same as forward charge — only the person liable to pay changes. The recipient can usually claim input tax credit of the GST paid under RCM.